Antipsychotic drugs anticholinergic effects

Phenothiazine antipsychotic drugs Anticholinergic effects Ca " channel blockade ... 

It is also very important, if possible, to discontinue or lower the doses of drugs with anticholinergic effects antihistamines, antipsychotics, antidepressants, uro-logic spasmolytics, anti-arrhythmics, drugs for Parkinson s disease and more. Prophylactic treatment against Candida infection, bacteria and caries can also be useful (Mouly et al. 2007). 

Tricyclic antidepressants are notorious for their risk to be involved in drug-drug interactions. Additive anticholinergic effects can be expected in combination with antihistamines, antipsychotics and anticholinergic-type anti-Parkinson agents. Hepatic enzyme-inducing agents increase their hepatic metabolism while enzyme inhibitors may potentiate the effects of tricyclics. Concomitant use with monoamine oxidase inhibitors will produce hypertension, hyperpyrexia and convulsions. 

Antipsychotics produce more important pharmacodynamic than pharmacokinetic interactions because of their multiple effects. Additive effects may occur when these drugs are combined with others that have sedative effects, a-adrenoceptor-blocking action, anticholinergic effects, and—for thioridazine and ziprasidone—quinidine-like action. 

FIGURE 11-8. Side effects of the conventional antipsychotics (part 1). In this diagram, the icon of a conventional antipsychotic drug is shown with its Ml anticholinergic-antimuscarinic portion inserted into acetylcholine receptors, causing the side effects of constipation, blurred mouth, dry mouth, and drowsiness. 

Tertiary-amine muscarinic receptor antagonists gain access to the central nervous system and are therefore the anticholinergic drugs used to treat parkinsonism and the extrapyramidal side effects of antipsychotic drugs. Specific agents used primarily for these conditions include benztropine mesylate (Cogentin) and trihexyphenidyl hydrochloride (Artane, others). 

Perhaps because of their anticholinergic effects (cf benztropine, Chapter 28 Pharmacologic Management of Parkinsonism Other Movement Disorders), some of the Hi antagonists have significant acute suppressant effects on the parkinsonism symptoms associated with certain antipsychotic drugs. 

Also note that the potential for an interaction between drugs does not preclude their concurrent use. Certain combinations are routinely prescribed without problems in many patients (as with lithium and antipsychotics), whereas others are contraindicated due to the severity of the interaction (for example, MAOIs and SSRIs). However, whenever psychiatric medications are coadministered, the additive potential of central nervous system depression and anticholinergic effects must be considered. 

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